The present invention relates to reflecting electro-magnetic energy from a passive source onto a proximate object, for example in order to reflect electro-magnetic energy from a weapon into a person in proximity to the weapon.
A passive radiator (also named a passive director or reflector) is a radio-frequency (RF) radiation element which does not have any wired input. Instead, it is coupled to radio waves radiated from another active antenna element, and reradiates (i.e. reflects) the RF energy. The reradiation pattern (also named herein the resonance profile) is determined by factors such as the dimensions and arrangement of the passive radiator or radiators, and other factors such as the transmitted frequency, the dielectric surrounding the reflecting object and spatial considerations. If properly configured, the passive radiator reflects the RF radiation in a predetermined and desired fashion.
The use of passive radiators is well known in antenna theory. A passive radiator is used in several types of antennas in order to shape the antenna pattern and bandwidth (see Allan W. Scott, “Understanding Microwave”, John Wiley and Sons, pp. 327-331, 1993, and Kai Cheng, “Encyclopedia of RF and Microwave Engineering” pp. 185-217, John Wiley and Sons, 2005).
For example, a typical parabolic antenna consists of a passive parabolic reflector illuminated by a small feed antenna (e.g. a dipole antenna). The parabolic reflector serves to direct the RF radiation emitted by the feed antenna (for example the torroidal radiation pattern of a dipole antenna) into a plane wave and to provide gain.
Another example of an antenna which utilizes passive radiators is the Yagi-Uda antenna. The Yagi-Uda antenna is a directional antenna consisting of an array of a dipole and additional passive radiators. The passive radiators serve as parasitic elements, which modify the dipole radiation pattern into a more directive pattern (e.g. the End-Fire far field pattern).
Passive radio-frequency identification (RFID) utilizes the scattering of RF radiation at certain frequencies to identify an RF tag that is placed between the RFID antennas. The power that is scattered by the RFID and its influence on nearby objects is a side effect which at times is undesired and problematic.
In current transmission systems the passive radiator serves as an antenna component for directing the RF transmission to a receiver (or receiving element). The passive radiator of the antenna is designed for predetermined system purposes and its characteristics are selected to fit predetermined criteria, and are appropriate for the RF transmission characteristics.
The Active Denial System (ADS) is a directed energy weapon developed by the US military. The ADS works by transmitting electromagnetic radiation at a frequency of 95 GHz toward the subjects. The waves excite water molecules in the skin, causing an intensely painful burning sensation. While not actually burning the skin, the burning sensation is similar to that of a light bulb being pressed against the skin (see David Hambling, 2006, “Techwatch-Forecasting Pain”, Popular Mechanics 183(12):32, ISSN 0032-4558). The frequency of 95 GHz was selected because it does not penetrate deeply into the body, thereby affecting external organs only, such as skin. The focused beam is considered effective for targets at a range of just under half a kilometer. A similar, lower-range system named the Silent Guardian™ has been developed by Raytheon.
The Active Denial System (ADS) is a directed energy weapon developed by the US military. The ADS works by transmitting electromagnetic radiation at a frequency of 95 GHz toward the subjects. The waves excite water molecules in the skin, causing an intensely painful burning sensation. While not actually burning the skin, the burning sensation is similar to that of a light bulb being pressed against the skin (see David Hambling, 2006, “Techwatch-Forecasting Pain”, Popular Mechanics 183(12):32, ISSN 0032-4558). The frequency of 95 GHz was selected because it does not penetrate deeply into the body, thereby affecting external organs only, such as skin. The focused beam is considered effective for targets at a range of just under half a kilometer. A similar, lower-range system named the Silent Guardian™ has been developed by Raytheon.
EM energy levels somewhat above 1 W/kg inside tissue may become significant or even damaging (see H. P. Schwan and K. R. Foster, “RF-Fields interactions with biological mechanisms”, Proc. IEEE 68:104-113 (1980)). The International Committee on Non-Ionizing Radiation Protection (ICNIRP) has set a limit of exposure to RF fields from far-field exposure to 10 W/m2. The U.S. F.C.C. organization had also set the same threshold value, which has been adopted in numerous countries worldwide (see M. H. Repacholi, “Radiofrequency electromagnetic-field exposures standards”, IEEE Eng. Med. Biol. 6:18-21 (1987)).